late 14c., "peaceable, at rest, restful, tranquil," from Old French quiet and directly from Latin quietus "calm, at rest, free from exertion," from quies (genitive quietis) "rest" (see quiet (n.)). As an adverb from 1570s. Related: Quietly; quietness.

v.

late 14c., "subdue, lessen," from quiet (adj.) and in part from Latin quietare. From mid-15c. as "to make silent, cause to be quiet;" intransitive sense of "become quiet, be silent" is from 1791. Related: Quieted; quieting.